A Sondheim premiere in New York! Besotted fans of one of the four greatest-ever Broadway composer-lyricists (the others being Irving Berlin, Frank Loesser and Cole Porter, all, regrettably, dead) were resigned never to seeing another. I feared that we were going to have to make do, perpetually, with repeated, indeed incessant, revivals of Sweeney Todd, and those anthologies, such as Side by Side by Sondheim and Putting It Together, which started out as such fun but became funerary lamentations for the lack of something novel, exciting and, most of all, unknown.Yet now, 14 years after Passion, Sondheim’s adaptation of an Italian film about an embarrassingly neurotic love affair, comes Road Show. I saw it a few days ago, shortly after its opening.